Image reading apparatus and assembling method

ABSTRACT

A document reading apparatus includes a sensor configured to receive light from a document, an imaging lens configured to form an image of light from the document on the sensor, a first holding member to which the imaging lens is fixed, and a second holding member to which the sensor is fixed, wherein the first holding member and the second holding member are fixed using an adhesive and solder.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/903,475, filed on May 28, 2013, the content of which isexpressly incorporated by reference herein in its entirety. Thisapplication also claims the benefit of Japanese Patent Application No.2012-123494 filed May 30, 2012, which are hereby incorporated byreference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image reading apparatus including animaging unit that forms an image of light from a document, and a imagesensor that receives the light from the document via the imaging unit,and a method for assembling the image reading apparatus.

2. Description of the Related Art

Conventionally, there is an image reading apparatus including an opticalunit as illustrated in FIG. 10. The optical unit uses an imaging unit toform an image of light from the document on a solid-state image sensor,and thus generates image data of the document.

In general, when the image reading apparatus is assembled, opticaladjustment is performed as follows.

Referring to FIG. 10, a solid-state image sensor 100 is mounted on asolid-state image sensor substrate 101. The solid-state image sensorsubstrate 101, on which the solid-state image sensor 100 has beenmounted, is fixed to a substrate holding member 102. An imaging unit 103is fixed to an optical unit frame 104. After the optical adjustment isperformed, the substrate holding member 102 is fixed to solid-stateimaging unit holding members 106 a and 106 b, which are fixed to theoptical unit frame 104. The position of the solid-state image sensor 100with respect to the imaging unit 103 is adjusted in performing theoptical adjustment.

More specifically, the substrate holding member 102 is temporarily heldby an adjustment tool (not illustrated). A gap of approximately 1 mm isthen formed between the substrate holding member 102 temporarily held bythe adjustment tool and the solid-state imaging unit holding members 106a and 106 b. The adjustment tool is then used to move the substrateholding member 102, to which the solid-state image sensor 100 is fixedvia the solid-state image sensor substrate 101. The position of thesolid-state image sensor 100 in X, Y, and θ directions is thus adjustedto adjust the focus on the solid-state image sensor 100.

Adhesives are then injected to and fixated in the gap between thesubstrate holding member 102 and the solid-state imaging unit holdingmembers 106 a and 106 b at fixed portions 107 a, 107 b, 107 c, and 107 din the adjusted position. As a result, the substrate holding member 102is fixed to the optical unit frame 104. In other words, the solid-stateimage sensor 100 and the imaging unit 103 are fixed to the optical frameunit in a focus-adjusted state. Adhesives, such as a naturally curableadhesive, an ultraviolet curable adhesive, and an instant adhesive, areused.

In recent years, the adhesive is automatically applied, and efficiencyis thus improved. However, since the adhesive is made of a material suchas acrylic resin and epoxy resin, there is a lack of strength.

Further, solder may be used as a fixing member instead of the adhesive.The fixing strength of the solder is sufficient. However, solderingneeds a skilled worker. For example, if a soldering iron is pressed onthe substrate holding member 102 while soldering, the position of thesubstrate holding member, which is only temporarily fixed by theadjustment tool, becomes displaced. Fixing using the solder is thusinefficient.

Furthermore, when the adhesive hardens, volume contraction occurs, sothat a relative distance between the solid-state image sensor 100 andthe imaging unit 103 is changed. As a result, focus variation occursbefore and after curing, and image degradation is generated. In recentyears, an increase in the pixel number of the solid-state image sensorhas made the solid state image sensor sensitive to changes in thefocusing. As a result, the defocusing amount caused by the change in thevolume when the adhesive hardens is not ignorable.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a document readingapparatus includes a sensor configured to receive light from a document,an imaging lens configured to form an image of light from the documenton the sensor, a first holding member to which the imaging lens isfixed, and a second holding member to which the sensor is fixed, whereinthe first holding member and the second holding member are fixed usingan adhesive and solder.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a substrate holding member.

FIG. 2 is a perspective view illustrating an imaging lens holdingmember.

FIG. 3 is a cross-sectional view illustrating an optical unit.

FIG. 4 is a cross-sectional view illustrating an image readingapparatus.

FIG. 5 is a perspective view illustrating an adjustment tool.

FIG. 6 is a graph illustrating a focus displacement amount.

FIG. 7 illustrates a modification example of a portion fixed using anadhesive and solder.

FIG. 8 illustrates the modification example of the portion fixed usingthe adhesive and the solder.

FIG. 9 illustrates the modification example of the portion fixed usingthe adhesive and the solder.

FIG. 10 is a perspective view illustrating a conventional optical unit.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiment of the invention will be described in detail belowwith reference to the drawings.

FIG. 4 is a cross-sectional view illustrating an image reading apparatusaccording to a first exemplary embodiment of the present invention. FIG.3 is a cross-sectional view illustrating an optical unit in the imagereading apparatus. FIG. 1 is a perspective view illustrating a substrateholding member in the optical unit. FIG. 2 is a perspective viewillustrating an imaging lens holding member in the optical unit.

Referring to FIG. 4, the image reading apparatus reads a documentpositioned on a document positioning glass plate 110 by moving theoptical unit in a moving direction. The optical unit is stored in areader frame 111, and a timing belt 113 driven by a motor moves theoptical unit along a guide shaft 112 in the moving direction indicatedby an arrow illustrated in FIG. 4.

Referring to FIG. 3, the optical unit includes an optical unit frame104, the imaging lens 103, plane mirrors 109 a, 109 b, 109 c, and 109 d,and a solid-state image sensor 100. The plane mirrors 109 a, 109 b, 109c, and 109 d guide to the imaging lens 103 the light, which isirradiated by an illumination unit (not illustrated) and reflected onthe document. The imaging lens 103 thus forms an image on thesolid-state image sensor 100. The solid-state image sensor 100 thengenerates an image signal, i.e., an electrical signal, based on thereceived reflected light. According to the present exemplary embodiment,a complementary metal-oxide semiconductor (CMOS) sensor is used as thesolid-state image sensor which receives the reflected light from thedocument and generates the image signal. A charge-coupled device (CCD)sensor may also be used as the solid-state image sensor.

Referring to FIG. 1, the solid-state image sensor substrate 101, onwhich the solid-state image sensor 100 is mounted, is fixed to thesubstrate holding member 102. According to the present exemplaryembodiment, the solid-state image sensor substrate 101 is fixed to thesubstrate holding member 102 by a screw. On the other hand, referring toFIG. 2, the imaging lens 103 including the lens is fixed to the imaginglens holding member 105. Further, the substrate holding member 102 isfixed to the imaging lens holding member 105, and the imaging lensholding member 105 is fixed to the optical unit frame. The substrateholding member 102 and the imaging lens holding member 105 are formed bybending a tinned steel plate.

When assembling, an assembling worker adjusts a positional relationbetween the imaging lens holding member 105 and the substrate holdingmember 102 so that the focus becomes adjusted. After performing theadjustment, the assembling worker fixes the substrate holding member 102to the imaging lens holding member 105 using the adhesive and thesolder. The assembling worker then fixes to the optical unit frame 104the imaging lens holding member 105 fixed to the substrate holdingmember 102.

The optical adjustment performed in assembling the optical unit will bedescribed below.

In the optical adjustment, the position of the solid-state image sensor100 with respect to the imaging lens 103 is adjusted. A gap ofapproximately 1 mm is formed in respective vertical and horizontal focusmoving directions in a connecting portion between the imaging lensholding member 105 and the substrate holding member 102, to allowadjustment. According to the present exemplary embodiment, an adjustmenttool illustrated in FIG. 5 is used to adjust the position of thesubstrate holding member 102, to which the solid-state image sensor 100is fixed, with respect to the imaging lens holding member 105 to whichthe imaging lens 103 is attached.

Referring to FIG. 5, an adjustment tool 200 includes a pedestal 204, towhich the imaging lens holding member 105 is temporarily fixed, and astage 203, to which the substrate holding member 102 is temporarilyfixed.

More specifically, the substrate holding member 102 is temporarily fixedusing left and right guide pins 201 a and 201 b to a clamp device 202attached to the stage 203. According to the present exemplaryembodiment, the solid-state image sensor substrate 101, on which thesolid-state image sensor 100 is mounted, is fixed to the substrateholding member 102.

The stage 203 adjusts the position of the substrate holding member 102in the X, Y, and θ directions. By adjusting the position of thesubstrate holding member 102 in the X, Y, and θ directions using thestage 203, the position of the solid-state image sensor 100 with respectto the imaging lens 103 can be adjusted so that the focus becomesadjusted.

The method for fixing to the imaging lens holding member 105 thesubstrate holding member 102, on which optical adjustment has beenperformed, will be described below.

An automatic injector device (not illustrated) injects the adhesive togaps as fixed portions 107 a and 107 b between the substrate holdingmember 102, on which optical adjustment has been performed, and theimaging lens holding member 105 that are temporarily fixed to theadjustment tool 200. After the adhesive has naturally hardened andreached practical strength, the worker fixes to the imaging lens holdingmember 105 the substrate holding member 102 using the solder atpositions 108 a and 108 b, which are different from the positions inwhich the adhesive has been injected. The positions 108 a and 108 bbound using the solder are near positions, as the fixed portions 107 aand 107 b, bound by the adhesive, respectively, and are within a rangein which the heat due to soldering is transferred.

When the solder cools down and is solidified, the binding strengthreaches the same level as the binding strength of metal welding. Thesubstrate holding member 102 and the imaging lens holding member 105 arethus directly and firmly bonded together without other members. As aresult, breakage or displacement of the fixed portions due to vibrationor impact can be prevented.

When soldering is performed, the substrate holding member 102 and theimaging lens holding member 105 are previously fixed to each other bythe adhesive. Thus, the displacement does not occur even if thesoldering iron touches the substrate holding member. In other words, thesoldering efficiency is improved as compared to the conventional casewhere the substrate holding member 102 and the imaging lens holdingmember 105 are fixed using only the solder. Further, since displacementrarely occurs in the soldering, it is not necessary to firmly performthe temporary fixation of the substrate holding member. As a result, theclamp device, such as a magnet clamp which is easily attachable anddetachable, may be used, so that efficiency can be further improved.

Furthermore, it is confirmed that a change in focusing before and afterthe adhesive has hardened can be reduced by setting a soldering bondingposition near an adhesive bonding position. FIG. 6 illustrates amountsof focusing position displacement when the substrate holding member 102and the imaging lens holding member 105 are fixed to each other usingthe adhesive and then by soldering, after the optical adjustment isperformed. Referring to FIG. 6, a vertical axis indicates an amount (μm)of displacement of the focusing position when the focusing positionbefore the adhesion (that is, after performing the optical adjustment)is set to zero. “Adhesion” indicated on a horizontal axis is timing atwhich the fixation is performed using the adhesive while the focusposition has been adjusted by the optical adjustment. “Soldering”indicates timing at which soldering is performed after the adhesive hasfixated. “After soldering” indicates timing at which the solder hasfixated. Lines No. 1, No. 2, No. 3, No. 4, No. 5, No. 6, No. 7, No. 8,and No. 9 each indicate results of the experiment. As illustrated inFIG. 6, the focusing position, which has been displaced due to volumecontraction caused by fixation of the adhesive, can be returned towardsthe zero position direction by performing soldering. Further, accordingto the present exemplary embodiment, the focusing position displacementbecomes less than or equal to ±10 μm, which is an appropriate rangethereof, in all of the nine experiment results. As described above, theeffect of volume contraction due to the hardening of the adhesive can bereduced by arranging the fixed portion using the solder near the fixedportion using the adhesive. It is assumed that such a phenomenon occursas follows. The heat caused by the soldering is transferred to thefixated adhesive, and the hardened adhesive expands. An anneal effectthen occurs on the hardened adhesive, and an internal distortion(residual stress) of the hardened adhesive is released, so that thefocusing position, which has been displaced due to the effect of thevolume contraction, returns towards the zero position direction.

Further, the solder-fixed portion acts as a ground between the substrateholding member 102 and the imaging lens holding member 105, and may thushold a margin with respect to static and electromagnetic interference(EMI) radiation noise.

The ultraviolet curable adhesive may be used as the adhesive. Theultraviolet curable adhesive hardens in a short time by being irradiatedwith the ultraviolet light, so that work time can be shortened. Further,an instant curable adhesive may be used as the adhesive. If there is agap which cannot be reached by the ultraviolet light, or a portion whichcannot be reached by the ultraviolet light due to a shadow of a shape,the substrate holding member 102 and the imaging lens holding member 105may be fixated in a shorter time by using the instant curable adhesiveinstead of the ultraviolet curable adhesive.

Further, the positions and the number of the adhesive-fixed portions andthe solder-fixed portions are not limited to the positions and thenumber illustrated in FIG. 2.

For example, as illustrated in FIG. 7, there may be four adhesive-fixedportions (107 a, 107 b, 107 c, and 107 d) and two solder-fixed portions(108 a and 108 b). Referring to FIG. 7, the solder-fixed portions arearranged to be approximately equidistant from the plurality of positionsbound using the adhesive. In other words, the position of thesolder-fixed portion 108 a is approximately equidistant from theadhesive-fixed portions 107 a and 107 b, and the position of thesolder-fixed portion 108 b is approximately equidistant from theadhesive-fixed portions 107 c and 107 d. By such an arrangement, theheat caused by performing the soldering is equally transferred to therespective adhesives, so that the anneal effect on each adhesive makesthe contraction amount due to the hardening uniform, and thus the changein focusing is further reduced.

Furthermore, as illustrated in FIG. 8, the worker can view from theimaging lens side of the adjustment tool the positions of theadhesive-fixed portions 107 a, 107 b, 107 c, and 107 d and thesolder-fixed portions 108 a and 108 b. When performing the opticaladjustment, the worker performs the adjustment while viewing from theimaging lens side. If the adhesive-fixed portions and the solder-fixedportions are arranged not to mutually become blind spots when the workerviews the adjustment tool from the imaging lens side, the efficiency canbe improved and failure to perform bonding may be prevented.

Moreover, as illustrated in FIG. 9, the positions of the adhesive-fixedportions 107 a, 107 b, 107 c, and 107 d and the solder-fixed portions108 a and 108 b are arranged approximately on an ellipse centered on anoptical axis of the lens in the imaging lens 103. According to theabove-described exemplary embodiment, the amount of displacement of thefocus position due to the volume contraction when the adhesive hardenscan be reduced. However, the amount of displacement cannot be reduced tozero. To solve such a problem, if the positions of the adhesive-fixedportions and the solder-fixed portions are arranged as illustrated inFIG. 9, the following may be achieved. The amount of displacement due tocontraction, which cannot be reduced according to the above-describedexemplary embodiment, becomes uniform in a main scanning direction or asub-scanning direction with respect to the imaging lens. In other words,a failure such as a one-sided blur can be prevented. The positions ofthe adhesive-fixed portions and the solder-fixed portions do not have tobe arranged approximately on an ellipse, but may be arrangedapproximately on a circle.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. A method for assembling an optical unit providedto a document reading apparatus for reading a document, the methodcomprising: adjusting a positional relation between a first holdingmember to which an imaging lens is fixed and a second holding member towhich a sensor substrate mounted with a sensor is fixed, so as to adjusta focus; fixing the first holding member and the second holding memberof which the positional relation are adjusted by using an adhesive; andsoldering the first holding member and the second holding member whichare fixed using the adhesive.
 2. The method for assembling according toclaim 1, wherein, in the adjusting, a position of the second holdingmember with respect to the first holding member is moved toward X and Ydirections which are perpendicular to an optical axis direction, and isrotated with respect to the optical axis direction
 3. The method forassembling according to claim 1, wherein the adhesive is ultravioletcuring-type adhesive.
 4. The method for assembling according to claim 1,wherein the first and second holding members are steel plates treatedwith tinning processing.
 5. The method for assembling according to claim1, wherein the position to be fixed with the adhesive and the positionto be soldered are different.